The effect of stressful employment on pregnancy outcome has been examined in this study of pregnancy outcomes among medical residents. Several studies of paid employment by women during pregnancy have shown an increased risk of both preterm birth and low birth weight associated with strenuous occupations. However, the majority of studies show no increased risk. None of the previous studies were able to control adequately for the socioeconomic status of the women, and in many instances improper controls were used. Women who become pregnant during medical residency are in many respects an optimal group in which to study this issue. They are universally highly educated and in many respects of high socioeconomic status, yet their occupation is highly stressful and physically demanding. For this reason, the effects of a mentally and physically demanding occupation can be studied independently of socioeconomic status. Spouses of male residents comprise an appropriate control group, as they are also of high socioeconomic status, but in most cases have less strenuous occupations than that of a medical resident. We hypothesize that the mentally and physically strenuous occupation of residency adversely effects the pregnancy outcomes of female residents, as compared to the pregnancy outcomes of spouses of male residents. The proposed study examined pregnancy outcomes among a cohort of 1985 medical school graduates. Approximately 10,000 residents (all of the women residents and a 50% random sample of male residents) were surveyed to determine the pregnancy outcomes of the female residents and spouses of male residents. Women residents were found not to be at increased risk of a variety of adverse pregnancy outcomes compared to spouses of male residents. These results suggest that much of the previously reported occupational influences on pregnancy outcomes were caused by unmeasured differences in socioeconomic status.